Method for preparing nanometer oxide by recycling rare earth mother liquor

Abstract

The application relates to a method for preparing nanometer oxides by recycling rare earth mother liquor. The method comprises the following steps in sequence: preparation of a precursor solution, uniform precipitation reaction, solid-liquid separation, calcination and recycling of the mother liquor; the composition of the precursor solution comprises soluble rare earth salt, precipitator, structure directing agent, deionized water and organic solvent; the heating mode in the uniform precipitation reaction comprises gradient heating; the mother liquor is added with a supplementary medium to obtain a recycled mother liquor in the recycling of the mother liquor; the supplementary medium comprises soluble rare earth salt, precipitator, structure directing agent and organic solvent which are consistent with the precursor solution; and the pH value of the recycled mother liquor is 4-10. In the method, the rare earth mother liquor containing low impurity concentration is added with a supplementary medium to realize recycling, the impurity concentration in the mother liquor is diluted by the supplementary medium, and thus the accumulation of impurities is avoided in the recycling process, and the recycling of the rare earth mother liquor is realized.

Description

Technical Field

[0001] This application belongs to the field of rare earth material preparation and industrial wastewater resource treatment technology, specifically involving rare earth mother liquor recycling and rare earth oxide preparation methods, and particularly a method for preparing nano-oxides by recycling rare earth mother liquor. Background Technology

[0002] Rare earth oxide nanomaterials, with their unique optical, electrical, and magnetic properties, have significant application value in numerous fields such as catalysis, luminescence, polishing, and ceramics. Currently, the main methods for preparing rare earth oxides include hydrothermal / solvothermal methods, thermal decomposition methods, and precipitation methods. Among these, the homogeneous precipitation method has outstanding advantages such as uniform product particle size, good dispersibility, and strong process controllability. Its basic principle is based on the hydrolysis reaction of urea under heating conditions: CO(NH2)2 + 3H2O → 2NH3·H2O + CO2, slowly releasing OH-. - and CO3 2- This method uniformly precipitates metal ions in solution as basic carbonates or carbonate precursors, which are then converted into oxides upon calcination. This method eliminates the particle size unevenness caused by excessively high local concentrations of the precipitant in direct precipitation methods. However, this method still faces a series of technical challenges that urgently need to be addressed in actual industrial production.

[0003] Firstly, there is the issue of mother liquor recycling and the continuous accumulation of impurities. The single-pass yield of precipitation reactions is typically between 70% and 85%, resulting in a still relatively high concentration of residual rare earth ions in the mother liquor after the reaction, reaching 0.02 mol / L to 0.05 mol / L, accounting for 15% to 20% of the total raw material. Directly discharging the mother liquor would not only cause a serious loss of rare earth resources but also lead to severe environmental pollution. If the mother liquor is directly recycled to improve the yield, with each cycle, impurity ions and unreacted organic matter in the mother liquor will continuously accumulate. This accumulation of impurities will significantly affect the quality of subsequent products, leading to a wider particle size distribution and poorer morphology of newly formed nanoparticles, thereby severely affecting the stability and consistency of product performance.

[0004] Furthermore, the consumption of organic solvents and the emission of volatile organic compounds (VOCs) pose potential threats to the production environment and human health. In existing processes, organic solvents such as ethylene glycol and methanol are typically added to effectively control the dispersibility of nanoparticles. However, these solvents have high single-pass loss rates, which not only increases the overall production cost but also carries the risk of VOC emissions.

[0005] To address the aforementioned issues, existing technologies have proposed various solutions, but all have significant limitations or shortcomings. CN101077790A discloses a method for preparing rare earth oxides using a homogeneous precipitation method of urease-catalyzed urea hydrolysis. While this method can proceed at relatively low temperatures, it does not address the core issue of mother liquor recycling, and the enzyme catalyst used is expensive, making it difficult to meet the needs of large-scale industrial applications. CN117446850A discloses a method for efficiently recovering rare earth oxides from rare earth wastewater, which uses alkaline solution and polyacrylamide for synergistic precipitation. However, this is essentially an end-of-pipe treatment technology, failing to achieve direct recycling of the mother liquor within the process system, and introducing new chemical reagents, increasing the complexity of subsequent treatment. CN1417127A discloses a method for preparing rare earth nano-oxides using bicarbonate precipitation combined with a dispersant. This method also fails to solve the problem of mother liquor recycling, and the dispersants used, such as sodium dodecylbenzenesulfonate, are prone to residues in the product, affecting the purity of the final product.

[0006] Therefore, developing a new green preparation method for nano-rare earth and metal oxides that can achieve efficient recycling of mother liquor, effectively solve the problem of continuous accumulation of impurities, and reduce the consumption of organic solvents has become an urgent problem to be solved in order to promote clean production and efficient utilization of resources in the rare earth industry. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for preparing nano-oxides through the recycling of rare earth mother liquor. The method provided in this application uses rare earth-containing wastewater generated during the rare earth separation and purification process as the mother liquor. Through the design of a recycling process, the rare earth elements in the mother liquor are enriched and recovered, and finally, the recovered rare earth elements are converted into rare earth oxide nanoparticles.

[0008] To achieve this objective, the present application adopts the following technical solution: In a first aspect, this application provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises soluble rare earth salts, precipitants, structure-directing agents, deionized water, and organic solvents. The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 4 to 10, for example, it can be 4, 5, 6, 7, 8, 9 or 10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0009] This application designs a rare earth mother liquor recycling process, in which rare earth mother liquor containing a low concentration of impurities is added to a replenishing medium and recycled. The replenishing medium effectively dilutes the concentration of impurities that accumulate in the rare earth mother liquor, while simultaneously replenishing fresh reaction medium. This avoids the one-way accumulation of impurities during the recycling process and achieves the recycling and reuse of rare earth mother liquor.

[0010] In some embodiments, the concentration of rare earth ions in the circulating mother liquor is 0.05 mol / L or higher, for example, it can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L or 0.2 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] In some embodiments, the molar ratio of precipitant to rare earth ions in the circulating mother liquor is 15:1 or higher, for example, it can be 15:1, 17:1, 19:1, 20:1, 25:1, 30:1, 35:1 or 40:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] In some embodiments, the pH of the circulating mother liquor is 5 to 7.

[0013] In some embodiments, the method includes the following steps: (1) Dissolve the soluble rare earth salt, precipitant and structure directing agent together in a mixed solvent of deionized water and organic solvent, and stir thoroughly to form a uniform precursor solution; (2) The precursor liquid described in step (1) is transferred to a closed reactor for uniform precipitation reaction. After the reaction is completed, it is aged to obtain the reaction mixture. (3) The reaction mixture described in step (2) is subjected to solid-liquid separation to obtain nano-oxide precursor and mother liquor respectively; the nano-oxide precursor is washed and the washing liquid is collected, and then the nano-oxide precursor is dried and calcined in sequence to obtain nano-oxide; (4) Add supplementary medium to the mother liquor in step (3) to obtain circulating mother liquor; then repeat steps (2) and (3) as circulating mother liquor for recycling.

[0014] In some embodiments, the soluble rare earth salt in step (1) includes at least one of rare earth nitrate, rare earth chloride, rare earth sulfate, or rare earth acetate.

[0015] In some embodiments, the rare earth element in the soluble rare earth salt of step (1) includes at least one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

[0016] In some embodiments, the rare earth ion concentration in the precursor solution in step (1) is 0.02 mol / L to 0.4 mol / L, for example, it can be 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L or 0.4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In some embodiments, the precipitant in step (1) includes urea.

[0018] In some embodiments, the structure directing agent in step (1) comprises polyvinylpyrrolidone, preferably PVP-K90.

[0019] In some embodiments, the molar ratio of the precipitant to rare earth ions in step (1) is 15:1 to 40:1, for example, it can be 15:1, 17:1, 18:1, 19:1, 20:1, 25:1, 30:1, 35:1 or 40:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 18:1 to 25:1.

[0020] In some embodiments, the concentration of the structure-directing agent in the precursor solution in step (1) is 5 g / L to 100 g / L, for example, it can be 5 g / L, 10 g / L, 15 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L or 100 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 10 g / L to 50 g / L.

[0021] In some embodiments, the organic solvent in step (1) includes at least one of ethylene glycol, glycerol, methanol or isopropanol, preferably at least one of ethylene glycol or methanol.

[0022] In some embodiments, the volume percentage of the organic solvent in the precursor solution in step (1) is 5% to 30%, for example, it can be 5%, 10%, 15%, 20%, 25% or 30%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 10% to 20%.

[0023] In some embodiments, the gradient heating in the homogeneous precipitation reaction in step (2) includes a first stage of heating, a second stage of heating, and a third stage of heating performed sequentially; The first stage of the gradient heating is heated to 70℃~80℃, and the holding time is 1h~2h. The second stage of the gradient heating process has a heating temperature of 80℃~90℃ and a holding time of 1h~6h. The third stage of the gradient heating process has a heating temperature of 90℃~100℃ and a holding time of 1h~5h.

[0024] The first stage of gradient heating has a heating temperature of 70℃~80℃, for example, it can be 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] The holding time for the first stage of gradient heating is 1h to 2h, for example, it can be 1h, 1.5h or 2h, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] The second stage of gradient heating has a heating temperature of 80℃~90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The holding time for the second stage of gradient heating is 1h to 6h, for example, it can be 1h, 2h, 3h, 4h, 5h or 6h, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] The third stage of gradient heating has a heating temperature of 90℃~100℃, for example, it can be 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] The holding time for the third stage of gradient heating is 1h to 5h, for example, it can be 1h, 2h, 3h, 4h or 5h, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] In some embodiments, the heating rate of the gradient heating is 0.5℃ / min to 5℃ / min, for example, it can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In some embodiments, the aging time after the uniform precipitation reaction in step (2) is 12h~24h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] In some embodiments, the centrifugation speed for solid-liquid separation in step (3) is above 8000 rpm, for example, it can be 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm or 10000 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In some embodiments, the centrifugation time for solid-liquid separation in step (3) is 10 min to 60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] In some embodiments, step (3) washing the nano-oxide precursor includes washing at least three times alternately with deionized water and anhydrous ethanol.

[0035] In some embodiments, the drying temperature in step (3) is 60°C to 80°C and the drying time is 8h to 15h.

[0036] The drying temperature in step (3) is 60℃~80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] The drying time in step (3) is 8h to 15h, for example, it can be 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] In some embodiments, the calcination temperature in step (3) is 300℃~1200℃ and the time is 1h~4h.

[0039] The calcination temperature in step (3) is 300℃~1200℃, for example, it can be 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃ or 1200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] The calcination time in step (3) is 1h to 4h, for example, it can be 1h, 2h, 3h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] In some embodiments, the calcined nano-oxide in step (3) includes at least one of Y2O3, Yb2O3, CeO2, La2O3, Gd2O3, Tb4O7, Lu2O3, Ni2O3 or Fe2O3.

[0042] In some embodiments, when the nano-oxide in step (3) is Y2O3 or Yb2O3, the calcination temperature is 850℃~950℃, for example, it can be 850℃, 870℃, 890℃, 900℃, 930℃ or 950℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] In some embodiments, when the nano-oxide in step (3) is CeO2, the calcination temperature is 750℃~850℃, for example, it can be 750℃, 770℃, 790℃, 800℃, 830℃ or 850℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In some embodiments, when the nano-oxide in step (3) is La2O3, the calcination temperature is 800℃~900℃, for example, it can be 800℃, 830℃, 850℃, 870℃, 890℃ or 900℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] In some embodiments, when the nano-oxide in step (3) is Gd2O3 or Tb4O7, the calcination temperature is 650℃~750℃, for example, it can be 650℃, 670℃, 690℃, 700℃, 730℃ or 750℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] In some embodiments, when the nano-oxide in step (3) is Lu2O3, the calcination temperature is 650℃~750℃, for example, it can be 650℃, 670℃, 690℃, 700℃, 730℃ or 750℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] In some embodiments, when the nano-oxide in step (3) is Ni2O3 or Fe2O3, the calcination temperature is 350℃~450℃, for example, it can be 350℃, 370℃, 390℃, 400℃, 430℃ or 450℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] In some embodiments, the mother liquor is recycled in step (4) 1 to 3 times, for example, 1, 2 or 3 times.

[0049] Secondly, this application also provides the application of the method described in the first aspect in the preparation of rare earth oxides and transition metal oxides.

[0050] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0051] Compared with the prior art, this application has the following advantages: (1) Improved utilization of rare earth resources: By implementing a recycling strategy, the rare earth elements in the mother liquor are enriched and recovered, and the recovered rare earth elements are finally converted into rare earth oxide nanoparticles with uniform particle size and good dispersion, thereby reducing the loss of rare earth resources from the source.

[0052] (2) Impurity control and product quality stability: The mother liquor recycling strategy, combined with precise feeding ratio, ensures that even after the mother liquor is recycled 1 to 3 times, the prepared nano-oxide products still meet the requirements of industrial-grade products for particle size and stability. Attached Figure Description

[0053] Figure 1 The process flow diagrams for Examples 1 to 11 of this application illustrate the rare earth mother liquor recycling process and main operating units.

[0054] Figure 2 SEM image of yttrium oxide nanoparticles prepared in Example 1.

[0055] Figure 3 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained in Example 1.

[0056] Figure 4 This is an SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 1.

[0057] Figure 5 This is a particle size distribution diagram of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 1.

[0058] Figure 6 This is a SEM image of the yttrium oxide nanoparticles obtained from the second recycling of Example 1.

[0059] Figure 7 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained from the second recycling of Example 1.

[0060] Figure 8 SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor for Comparative Example 1.

[0061] Figure 9 The particle size distribution of yttrium oxide nanoparticles prepared by recycling the mother liquor of Comparative Example 1 is shown in the figure.

[0062] Figure 10 SEM image of yttrium oxide nanoparticles prepared in Example 2.

[0063] Figure 11 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained in Example 2.

[0064] Figure 12 This is an SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 2.

[0065] Figure 13 This is a particle size distribution diagram of yttrium oxide nanoparticles obtained by recycling the mother liquor in Example 2.

[0066] Figure 14 SEM images of yttrium oxide nanoparticles prepared when the mother liquor was recycled and the urea molar ratio was reduced to 15:1, for Comparative Example 2.

[0067] Figure 15 The particle size distribution diagram of the yttrium oxide nanoparticles obtained in Comparative Example 2 is shown.

[0068] Figure 16 SEM image of lutetium oxide nanoparticles prepared in Example 3.

[0069] Figure 17 This is a particle size distribution diagram of the lutetium oxide nanoparticles obtained in Example 3.

[0070] Figure 18 This is a SEM image of lutetium oxide nanoparticles prepared by recycling the mother liquor in Example 3.

[0071] Figure 19This is a particle size distribution diagram of lutetium oxide nanoparticles obtained by recycling the mother liquor in Example 3.

[0072] Figure 20 SEM image of yttrium oxide nanoparticles prepared using PVP-K60 for Comparative Example 3.

[0073] Figure 21 The particle size distribution diagram of the yttrium oxide nanoparticles obtained in Comparative Example 3 is shown.

[0074] Figure 22 SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor of Comparative Example 3.

[0075] Figure 23 The particle size distribution diagram is shown for the yttrium oxide nanoparticles obtained by recycling the mother liquor of Comparative Example 3.

[0076] Figure 24 This is a SEM image of lanthanum oxide prepared in Example 4.

[0077] Figure 25 The particle size distribution diagram is shown for lanthanum oxide prepared in Example 4.

[0078] Figure 26 The image shows a SEM image of lanthanum oxide obtained by direct recycling of the mother liquor in Comparative Example 4.

[0079] Figure 27 The particle size distribution of lanthanum oxide obtained by direct recycling of the mother liquor in Comparative Example 4 is shown.

[0080] Figure 28 This is a SEM image of the yttrium oxide nanoparticles prepared in Example 5.

[0081] Figure 29 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained in Example 5.

[0082] Figure 30 This is a SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 5.

[0083] Figure 31 This is a particle size distribution diagram of yttrium oxide nanoparticles obtained by recycling the mother liquor in Example 5.

[0084] Figure 32 SEM image of yttrium oxide nanoparticles prepared in Example 6.

[0085] Figure 33 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained in Example 6.

[0086] Figure 34 This is a SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 6.

[0087] Figure 35 This is a particle size distribution diagram of yttrium oxide nanoparticles obtained by recycling the mother liquor in Example 6.

[0088] Figure 36 This is an SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 7.

[0089] Figure 37 This is a particle size distribution diagram of yttrium oxide nanoparticles obtained by recycling the mother liquor in Example 7.

[0090] Figure 38 SEM image of yttrium oxide nanoparticles prepared in the high-concentration system of Example 11.

[0091] Figure 39 This is a particle size distribution diagram of the yttrium oxide nanoparticles obtained in Example 11.

[0092] Figure 40 This is a SEM image of yttrium oxide nanoparticles prepared by recycling the mother liquor in Example 11.

[0093] Figure 41 This is a particle size distribution diagram of yttrium oxide nanoparticles obtained by recycling the mother liquor in Example 11. Detailed Implementation

[0094] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0095] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0096] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0097] The term "embodiment" as used in this application means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0098] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0099] In this application, open-ended technical features or solutions described with terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both technical features or solutions where "A consists of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0100] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0101] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0102] In this application, "room temperature" generally refers to 4℃~35℃, and may refer to 20℃±5℃. In some embodiments of this application, room temperature refers to 20℃~30℃.

[0103] Unless otherwise specified, all reagents used in the examples and comparative examples in this application are commercially available analytical grade reagents.

[0104] Example 1 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor, and the process flow diagram is shown below. Figure 1 As shown, the method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0105] The method includes the following steps: (1) Dissolve 0.05 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 1.0 mol urea, and 8 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 450 mL deionized water and 50 mL ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.1 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 16 g / L, and ethylene glycol accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 12 h.

[0106] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0107] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0108] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using approximately 500 mL of the mother liquor obtained after centrifugation, 0.05 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.0 mol of urea, 20 g of PVP-K90, and 20 mL of ethylene glycol were added to maintain the Y... 3+ Concentration 0.1 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0109] The resulting mother liquor was recycled once, using 250 mL of the mother liquor, and supplemented with 0.05 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 1 mol of urea, 10 g of PVP-K90, and 20 mL of ethylene glycol to maintain Y... 3+ Concentration 0.1 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. The mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover the rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0110] Figure 2 and Figure 3 The images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 4 and Figure 5 The images and particle size distribution diagrams are SEM images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared by the first mother liquor recycling in step (4) of this embodiment. Figure 6 and Figure 7 The images shown are SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by the second mother liquor recycling in step (4) of this embodiment. It can be seen that although the yield is reduced, the particle size of the nanoparticles prepared by the two mother liquor recycling is similar to that of the precursor solution.

[0111] Example 2 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol and methanol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0112] The method includes the following steps: (1) Dissolve 0.1 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 2.0 mol urea, and 25 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 400 mL deionized water, 50 mL ethylene glycol, and 50 mL methanol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol and methanol each accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 12 h.

[0113] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0114] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0115] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 400 mL of mother liquor, 0.1 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 2.0 mol of urea, 35 g of PVP-K90, 50 mL of ethylene glycol and 50 mL of methanol were added to maintain the Y... 3+ Concentration 0.2 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0116] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 1 hour.

[0117] Figure 10 and Figure 11The images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 12 and Figure 13 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor in this embodiment. It can be seen that the nanoparticles prepared using a mixed solvent of ethylene glycol and methanol are smaller in size and more uniformly distributed than those prepared using ethylene glycol alone. The nanoparticles obtained by recycling the mother liquor are also smaller in size than those prepared using the precursor solution.

[0118] Example 3 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (lutetium chloride hydrate), a precipitant (urea), a structure directing agent (PVP-K90), deionized water, and an organic solvent (isopropanol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0119] The method includes the following steps: (1) Dissolve 0.005 mol lutetium chloride hydrate LuCl3·6H2O, 0.125 mol urea, and 5 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 190 mL deionized water and 10 mL isopropanol to prepare a precursor solution with a rare earth ion concentration of 0.05 mol / L. The urea and LuCl3 hydrate are mixed in the solution. 3+ The molar ratio was 25:1, the concentration of PVP-K90 was 50 g / L, and isopropanol accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 18 h.

[0120] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 4 hours, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0121] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 700℃ with a heating rate of 1℃ / min and held at 70℃ for 2 h to obtain lutetium oxide nanoparticles.

[0122] (4) Preparation of lutetium oxide nanoparticles by recycling the mother liquor. Using 180 mL of mother liquor, 200 mL of deionized water, and 20 mL of isopropanol, 0.005 mol of lutetium chloride hydrate (LuCl3·6H2O), 0.125 mol of urea, and 10 g of PVP-K90 were added to maintain the Lu... 3+ Concentration 0.05 mol / L, urea and Lu 3+ The molar ratio was 25:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 18 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain lutetium oxide nanoparticles.

[0123] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 5 hours; the calcination conditions are: calcination at 700℃, heating rate of 5℃ / min, and holding for 2 hours.

[0124] Figure 16 and Figure 17 The images and particle size distribution diagrams of the lutetium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 18 and Figure 19 The images shown are SEM images and particle size distribution diagrams of lutetium oxide nanoparticles prepared by recycling the mother liquor in this embodiment. It can be seen that the yield of mother liquor recycling is slightly reduced, and the particle size of nanoparticles prepared by mother liquor recycling is larger than that prepared by precursor solution.

[0125] Example 4 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (lanthanum nitrate hydrate), a precipitant (urea), a structure directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0126] The method includes the following steps: (1) Dissolve 0.02 mol of lanthanum nitrate hydrate La(NO3)3·6H2O, 0.4 mol of urea, and 10 g of polyvinylpyrrolidone PVP-K90 in a mixed solvent of 90 mL of deionized water and 10 mL of ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and La... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 16 h.

[0127] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient temperature program was used to carry out a homogeneous precipitation reaction: first, it was kept at 70°C for 1 hour, and then the temperature was increased to 80°C and kept at 8 hours; after the reaction was completed, it was aged for 16 hours.

[0128] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 800℃ with a heating rate of 0.5℃ / min for 6 h to obtain lanthanum oxide nanoparticles.

[0129] (4) Preparation of lanthanum oxide nanoparticles by recycling the mother liquor. Using 100 mL of mother liquor, 350 mL of washing solution, and 100 mL of ethylene glycol, 0.02 mol of lanthanum nitrate hydrate (La(NO3)3·6H2O), 0.4 mol of urea, and 10 g of PVP-K90 were added to maintain the La content. 3+ Concentration 0.2 mol / L, urea and La 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 16 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover the rare earth mother liquor and obtain lanthanum oxide nanoparticles.

[0130] The gradient heating program is as follows: first, maintain the temperature at 80℃ for 1 hour, then raise the temperature to 90℃ and maintain it for 4 hours.

[0131] Figure 24 and Figure 25 The images shown are SEM images and particle size distribution diagrams of lanthanum oxide prepared in step (3) of this embodiment. The lanthanum oxide nanoparticles are 237 nm in size.

[0132] Example 5 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0133] The method includes the following steps: (1) Dissolve 0.1 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 2.0 mol urea, and 25 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 400 mL deionized water and 100 mL ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol accounted for 20% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 12 h.

[0134] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0135] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0136] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 100 mL of mother liquor, 350 mL of washing solution, and 100 mL of ethylene glycol, 0.05 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 0.7 mol of urea, and 8 g of PVP-K90 were added. 3+ Concentration 0.1 mol / L, urea and Y 3+The molar ratio was 15:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover the rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0137] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 1 hour.

[0138] Figure 28 and Figure 29 The images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 30 and Figure 31 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor in this embodiment. It can be seen that the yield and particle size of the nano-oxide prepared by adding supplementary medium to the mother liquor and mixing it with the washing liquid and recycling it are improved compared with those prepared by the precursor liquid.

[0139] Example 6 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol and methanol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0140] The method includes the following steps: (1) Dissolve 0.2 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 4.0 mol urea, and 50 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 800 mL deionized water, 100 mL ethylene glycol, and 100 mL methanol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol and methanol each accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 18 h.

[0141] (2) The above precursor liquid was placed in a closed reactor equipped with a condenser reflux device, and a homogeneous precipitation reaction was carried out by a gradient heating program: first, it was kept at 80℃ for 1h, then heated to 90℃ for 2h, and finally heated to 100℃ for 4h; after the reaction was completed, it was aged for 18h.

[0142] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0143] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 400 mL of mother liquor, add 0.1 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 2 mol of urea, 25 g of PVP-K90, 50 mL of ethylene glycol, and 50 mL of methanol. 3+ Concentration 0.2 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0144] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 2 hours, and finally raise the temperature to 100℃ and hold for 3 hours.

[0145] Figure 32 and Figure 33 The images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 34 and Figure 35 The images shown are SEM images of yttrium oxide nanoparticles prepared by recycling the mother liquor in this embodiment. It can be seen that the nano-oxide particles prepared by scaling up to 1L and recycling the mother liquor have small particle size and are uniformly dispersed. This indicates that after scaling up to 1L, the yield and product quality remain stable, and the method is feasible for large-scale preparation of nano-oxide particles.

[0146] Example 7 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol and methanol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0147] The method includes the following steps: (1) Dissolve 0.2 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 4.0 mol urea, and 50 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 800 mL deionized water, 100 mL ethylene glycol, and 100 mL methanol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol and methanol each accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 18 h.

[0148] (2) The above precursor liquid was placed in a closed reactor equipped with a condenser reflux device, and a homogeneous precipitation reaction was carried out by a gradient heating program: first, it was kept at 80℃ for 1h, then heated to 90℃ for 2h, and finally heated to 100℃ for 4h; after the reaction was completed, it was aged for 18h.

[0149] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0150] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 400 mL of mother liquor, add 0.15 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 3 mol of urea, 48 g of PVP-K90, 50 mL of ethylene glycol, and 50 mL of methanol. 3+ Concentration 0.3 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0151] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 2 hours, and finally raise the temperature to 100℃ and hold for 3 hours.

[0152] Figure 36 and Figure 37 The images shown are SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor and increasing the concentration in step (4) of this embodiment. It can be seen that the yield of mother liquor recycling has been improved compared with Example 6, and the particle size of the obtained nano-oxide particles has increased.

[0153] Example 8 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 6.5.

[0154] The method includes the following steps: (1) Dissolve 4 mol of yttrium nitrate hydrate Y(NO3)3·6H2O, 80 mol of urea, and 1 kg of polyvinylpyrrolidone PVP-K90 in a mixed solvent of 16 L of deionized water and 4 L of ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol accounted for 20% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 24 h.

[0155] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient temperature program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80℃ for 0.75h, then the temperature was raised to 90℃ and kept for 2h, and finally the temperature was raised to 100℃ and kept for 4h; after the reaction was completed, it was aged for 24h.

[0156] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 60 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0157] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 100 mL of mother liquor, add 0.01 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 0.2 mol of urea, 2.5 g of PVP-K90, and 100 mL of deionized water. 3+ Concentration 0.005 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 6.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0158] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 2 hours, and finally raise the temperature to 100℃ and hold for 3 hours.

[0159] Example 9 This embodiment uses the mother liquor obtained in Example 8 for recycling to prepare yttrium oxide nanoparticles. The specific method is as follows: 300 mL of mother liquor is used, and 0.1 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.5 mol of urea, 15 g of PVP-K90, and 200 mL of deionized water are added. 3+ Concentration 0.2 mol / L, urea and Y 3+ The molar ratio was 15:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor, which was then stirred and dissolved at room temperature for 18 h; the above circulating mother liquor was subjected to a uniform precipitation reaction.

[0160] After the reaction was completed, the mixture was centrifuged at 9000 rpm for 60 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 60 °C for 12 h, and then calcined at 900 °C at a heating rate of 1 °C / min for 3 h to obtain white yttrium oxide nanoparticles.

[0161] The gradient heating program in the homogeneous precipitation reaction is as follows: first, hold at 80℃ for 2 hours, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 4 hours.

[0162] Example 10 This embodiment uses the mother liquor obtained in Example 8 for recycling to prepare yttrium oxide nanoparticles. The specific method is as follows: 300 mL of mother liquor is used, and 0.1 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.5 mol of urea, 15 g of PVP-K90, and 200 mL of deionized water are added. 3+ Concentration 0.2 mol / L, urea and Y 3+The molar ratio was 15:1. After adding supplementary medium, a circulating mother liquor was obtained with a pH of 9.5. The mother liquor was then stirred and dissolved at room temperature for 18 hours. The circulating mother liquor was then subjected to a uniform precipitation reaction.

[0163] After the reaction was completed, the mixture was centrifuged at 9000 rpm for 60 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 60 °C for 12 h, and then calcined at 900 °C at a heating rate of 1 °C / min for 3 h to obtain white yttrium oxide nanoparticles.

[0164] The gradient heating program in the homogeneous precipitation reaction is as follows: first, hold at 80℃ for 2 hours, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 4 hours.

[0165] Example 11 This embodiment provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0166] The method includes the following steps: (1) Dissolve 0.2 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 3.5 mol urea, and 50 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 400 mL deionized water and 100 mL ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.35 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 100 g / L, and ethylene glycol accounted for 20% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 18 h.

[0167] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 3 hours, and finally heated to 100°C for 2 hours; after the reaction was completed, it was aged for 18 hours.

[0168] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 60 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0169] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 150 mL of mother liquor, add 0.019 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 0.4 mol of urea, 4 g of PVP-K90, 0.5 g of carbon black, 50 mL of deionized water, and 50 mL of ethylene glycol. 3+ Concentration 0.077 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0170] The centrifugation conditions were: 9000 rpm, 30 min, with carbon black as the centrifugation aid; The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 1 hour, and finally raise the temperature to 100℃ and hold for 3 hours.

[0171] Figure 38 and Figure 39 The images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this embodiment are shown below. Figure 40 and Figure 41 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor in this embodiment. It can be seen that the nano-oxide particles prepared by the precursor and mother liquor with high rare earth ion concentrations have a lower single-pass yield but smaller particle size, which increases the difficulty of centrifugation separation.

[0172] Comparative Example 1 This comparative example provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0173] The method includes the following steps: (1) Dissolve 0.05 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 1.0 mol urea, and 8 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 450 mL deionized water and 50 mL ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.1 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 16 g / L, and ethylene glycol accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 12 h.

[0174] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0175] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0176] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using approximately 500 mL of the mother liquor obtained after centrifugation, 0.05 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.0 mol of urea, 20 g of PVP-K90, and 20 mL of ethylene glycol were added to maintain the Y... 3+ Concentration 0.1 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. The mother liquor was then stirred and dissolved at room temperature for 12 h. Steps (2) and (3) were repeated with the above circulating mother liquor to recover rare earth mother liquor and obtain yttrium oxide nanoparticles. The obtained mother liquor was then recycled.

[0177] When the mother liquor is recycled again, 250 mL of mother liquor is used without adding any fresh rare earth salts, precipitants, structure directing agents and organic solvents. The reaction is carried out according to the heating procedure in step (2). After aging for 18 hours, solid-liquid separation, washing, drying and calcination are performed to obtain yttrium oxide nanoparticles.

[0178] Figure 8 and Figure 9 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor without adding fresh raw materials, as shown in the comparative example. It can be seen that the recycling yield of the mother liquor without adding rare earth ions and precipitants is significantly reduced, and the resulting nano-oxide particles have larger particle sizes and poorer dispersibility.

[0179] Comparative Example 2 This comparative example provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol and methanol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0180] The method includes the following steps: (1) Dissolve 0.1 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 2.0 mol urea, and 25 g polyvinylpyrrolidone PVP-K90 in a mixed solvent of 400 mL deionized water, 50 mL ethylene glycol, and 50 mL methanol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol and methanol each accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 12 h.

[0181] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 3 hours; after the reaction was completed, it was aged for 18 hours.

[0182] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0183] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 250 mL of mother liquor and 250 mL of washing solution, 0.1 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.5 mol of urea, and 100 mL of ethylene glycol were added. PVP-K90 was not added. The urea and Y... 3+ The molar ratio was 15:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover the rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0184] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 1 hour.

[0185] Figure 14 and Figure 15 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared when the mother liquor was recycled and the molar ratio of urea to rare earth ions was reduced to 15:1. It can be seen that when the molar ratio of precipitant to rare earth ions is reduced and the structure-directing agent is insufficient, the yield of mother liquor recycling decreases significantly and the particle size of the prepared nano-oxide particles increases.

[0186] Comparative Example 3 This comparative example provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (yttrium nitrate hydrate), a precipitant (urea), a structure-directing agent (PVP-K60), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 5.5.

[0187] The method includes the following steps: (1) Dissolve 0.1 mol yttrium nitrate hydrate Y(NO3)3·6H2O, 2.0 mol urea, and 50 g polyvinylpyrrolidone PVP-K60 in a mixed solvent of 400 mL deionized water and 100 mL ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and Y... 3+The molar ratio was 20:1, the concentration of PVP-K60 was 50 g / L, and ethylene glycol accounted for 20% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 24 h.

[0188] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient heating program was used to carry out a homogeneous precipitation reaction: first, it was kept at 80°C for 1 hour, then heated to 90°C for 1 hour, and finally heated to 100°C for 4 hours; after the reaction was completed, it was aged for 18 hours.

[0189] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 900℃ with a heating rate of 1℃ / min and held at that temperature for 3 h to obtain white yttrium oxide nanoparticles.

[0190] (4) Preparation of yttrium oxide nanoparticles by recycling the mother liquor. Using 150 mL of mother liquor, add 0.19 mol Y(NO3)3·6H2O of yttrium nitrate hydrate, 0.4 mol of urea, 4 g of PVP-K90, 100 mL of deionized water, and 50 mL of ethylene glycol. 3+ Concentration 0.077 mol / L, urea and Y 3+ The molar ratio was 20:1, and the pH of the mother liquor was adjusted to 5.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. Then, the mother liquor was stirred and dissolved at room temperature for 12 h. The above circulating mother liquor was used to repeat steps (2) and (3) to recover rare earth mother liquor and obtain yttrium oxide nanoparticles.

[0191] The gradient heating program is as follows: first, hold at 80℃ for 1 hour, then raise the temperature to 90℃ and hold for 1 hour, and finally raise the temperature to 100℃ and hold for 3 hours.

[0192] Figure 20 and Figure 21 The images shown are SEM images and particle size distribution diagrams of the yttrium oxide nanoparticles prepared in step (3) of this comparative example. Figure 22 and Figure 23 The images show SEM images and particle size distribution diagrams of yttrium oxide nanoparticles prepared by recycling the mother liquor in this comparative example. It can be seen that the dispersion and stabilization effect of PVP-K60 is worse than that of PVP-K90, and the resulting nano-oxide particles have larger particle sizes and poorer dispersibility.

[0193] Comparative Example 4 This comparative example provides a method for preparing nano-oxides by recycling rare earth mother liquor. The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises a soluble rare earth salt (lanthanum nitrate hydrate), a precipitant (urea), a structure directing agent (PVP-K90), deionized water, and an organic solvent (ethylene glycol). The heating method in the homogeneous precipitation reaction includes gradient heating. The pH value of the circulating mother liquor is 5.5.

[0194] The method includes the following steps: (1) Dissolve 0.02 mol of lanthanum nitrate hydrate La(NO3)3·6H2O, 0.4 mol of urea, and 10 g of polyvinylpyrrolidone PVP-K90 in a mixed solvent of 90 mL of deionized water and 10 mL of ethylene glycol to prepare a precursor solution with a rare earth ion concentration of 0.2 mol / L. The urea and La... 3+ The molar ratio was 20:1, the concentration of PVP-K90 was 50 g / L, and ethylene glycol accounted for 10% of the total volume of the mixed solvent. The mixture was stirred and dissolved at room temperature for 16 h.

[0195] (2) The above precursor liquid was placed in a closed reactor equipped with a reflux condenser and a gradient temperature program was used to carry out a homogeneous precipitation reaction: first, it was kept at 70°C for 1 hour, and then the temperature was increased to 80°C and kept at 8 hours; after the reaction was completed, it was aged for 16 hours.

[0196] (3) After the reaction was completed, the mixture was centrifuged at 9000 rpm for 30 min, and the nano-oxide precursor and mother liquor were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 70℃ for 12 h, and then calcined at 800℃ with a heating rate of 0.5℃ / min for 6 h to obtain lanthanum oxide nanoparticles.

[0197] (4) Preparation of lanthanum oxide nanoparticles by recycling the mother liquor. Use 100 mL of mother liquor, add 100 mL of deionized water, without adding lanthanum nitrate hydrate, urea and PVP-K90, adjust the pH of the mother liquor to 5.5 with 14.5 mol / L nitric acid to obtain recycled mother liquor, and then stir and dissolve at room temperature for 16 h; repeat steps (2) and (3) with the above recycled mother liquor to recover rare earth mother liquor and obtain lanthanum oxide nanoparticles.

[0198] The gradient heating program is as follows: first, maintain the temperature at 80℃ for 1 hour, then raise the temperature to 90℃ and maintain it for 4 hours.

[0199] Figure 26 and Figure 27 The images show SEM images and particle size distribution diagrams of lanthanum oxide obtained by direct recycling of the mother liquor in this comparative example. It can be seen that when the mother liquor is recycled directly without the addition of a replenishing medium, the yield is significantly reduced and the particle size of the nano-oxide particles increases.

[0200] Comparative Example 5 This comparative example uses the mother liquor obtained in Example 8 for recycling to prepare yttrium oxide nanoparticles. Specifically, 300 mL of mother liquor is used, and 0.1 mol of yttrium nitrate hydrate (Y(NO3)3·6H2O), 1.5 mol of urea, 15 g of PVP-K90, and 200 mL of deionized water are added. 3+ Concentration 0.2 mol / L, urea and Y 3+ The molar ratio was 15:1, and the pH of the mother liquor was adjusted to 2.5 with 14.5 mol / L nitric acid to obtain a circulating mother liquor. The mother liquor was then stirred and dissolved at room temperature for 18 hours. The circulating mother liquor was then subjected to a uniform precipitation reaction.

[0201] After the reaction was completed, the mixture was centrifuged at 9000 rpm for 60 min, and the nano-oxide precursor, pure mother liquor, and washing liquid were collected separately. The nano-oxide precursor was washed three times with deionized water and three times with anhydrous ethanol, dried at 60 °C for 12 h, and then calcined at 900 °C at a heating rate of 1 °C / min for 3 h to obtain white yttrium oxide nanoparticles.

[0202] The gradient heating program in the homogeneous precipitation reaction is as follows: first, hold at 80℃ for 2 hours, then raise the temperature to 90℃ and hold for 3 hours, and finally raise the temperature to 100℃ and hold for 4 hours.

[0203] Test Example 1 The nano-oxides obtained in Examples 1-11 and Comparative Examples 1-5 were characterized by SEM and their particle size distribution was measured. The test results are as follows: Figures 2-37 As shown in Table 1, the theoretical yield, actual yield, yield, and particle size test results of the obtained nano-oxides are presented.

[0204] In all embodiments of this application, the cycle yield is calculated based on the theoretical yield when the fresh rare earth salt added in that reaction is completely converted; the theoretical yield of the product and the reaction yield are calculated according to the following formulas: In all examples, “theoretical yield” refers to the maximum possible yield assuming that rare earth ions in the reaction system are completely converted into the corresponding oxides; the weight of the actual product in all examples was obtained by weighing with an electronic balance.

[0205] Table 1 Based on the above test results, it can be seen that: (1) As can be seen from Examples 1 to 11, this application designs a rare earth mother liquor recycling process, which adds a supplementary medium to the rare earth mother liquor containing a low concentration of impurities and then recycles it. The supplementary medium dilutes the impurity concentration in the mother liquor and simultaneously replenishes the reaction raw materials of the same type as the precursor liquid, thereby avoiding the one-way accumulation of impurities during the recycling process. The nano-oxide particles prepared by recycling the mother liquor have small particle size and are uniformly dispersed. The average particle size range of the nano-oxide is 55nm~237nm.

[0206] (2) By comparing Example 1 with Comparative Example 1 and Example 4 with Comparative Example 4, it can be seen that when the mother liquor is recycled, no soluble rare earth salts, precipitants and other supplementary media are added, resulting in the accumulation of impurities in the mother liquor, insufficient concentration of rare earth ions and precipitants, reduced yield of the prepared nano-oxides, increased particle size, and an average particle size of 160nm~248nm.

[0207] (3) By comparing Example 2 with Comparative Example 2, it can be seen that if no structure-directing agent is added during the recycling of the mother liquor, the precipitated particles will agglomerate, the centrifugation separation efficiency will decrease, and the yield will be lower than that of Example 2, which proves that PVP-K90 has a dispersing and stabilizing effect in the recycling of the mother liquor. By comparing Example 5 with Comparative Example 3, it can be seen that when the structure-directing agent is PVP-K60, the prepared nano-oxide particles have a large size and poor dispersibility, which proves that the dispersing and stabilizing effect of PVP-K90 is better than that of PVP-K60.

[0208] (4) By comparing Examples 8 to 10 with Comparative Example 5, it can be seen that the pH value during the mother liquor recycling process affects the particle size and dispersibility of the final obtained nano-oxides. When the pH of the mother liquor in this application is neutral or weakly acidic, the obtained nano-oxides have smaller particle size and better dispersibility. However, when the pH of the mother liquor is as low as 2 to 3, although the yield is improved, the particle size of the obtained nano-oxides increases, with an average particle size of 148 nm and poor dispersibility. When the pH of the mother liquor is 4 to 10, the average particle size of the obtained nano-oxides is 83 nm to 110 nm; when the pH of the mother liquor is 5 to 7, the obtained nano-oxides have the best particle size, with an average particle size of 83 nm to 86 nm and good dispersibility.

[0209] In summary, this application designs a rare earth mother liquor recycling process, using rare earth-containing wastewater generated during rare earth separation and purification as a raw material solvent. The rare earth mother liquor with a low impurity concentration is added to a replenishing medium and then recycled. The replenishing medium effectively dilutes the continuously accumulating impurity concentration in the mother liquor, while simultaneously replenishing fresh reaction raw materials. The concentration of rare earth ions, the molar ratio of precipitant to rare earth ions, the structural orientation and content, and the pH of the mother liquor are controlled. This avoids the unidirectional accumulation of impurities during the recycling process and realizes the recycling and reuse of rare earth mother liquor. Nano-oxides with uniform particle size and good dispersibility are prepared, and the feasibility of large-scale preparation is demonstrated.

[0210] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing nano-oxides by recycling rare earth mother liquor, characterized in that, The method includes sequentially performing the following steps: preparation of precursor solution, uniform precipitation reaction, solid-liquid separation, calcination, and recycling of mother liquor. The precursor solution comprises soluble rare earth salts, precipitant, structure directing agent, deionized water, and organic solvent. The heating method in the homogeneous precipitation reaction includes gradient heating. In the process of mother liquor recycling, a supplementary medium is added to the mother liquor to obtain recycled mother liquor; The supplementary medium includes: soluble rare earth salts, precipitants, structure-directing agents, and organic solvents of the same type as the precursor solution; The pH value of the circulating mother liquor is 4~10.

2. The method according to claim 1, characterized in that, The concentration of rare earth ions in the circulating mother liquor is above 0.05 mol / L; And / or, in the circulating mother liquor, the molar ratio of precipitant to rare earth ions is 15:1 or higher; And / or, the pH of the circulating mother liquor is 5 to 7.

3. The method according to claim 1 or 2, characterized in that, The method includes the following steps: (1) Dissolve the soluble rare earth salt, precipitant and structure directing agent together in a mixed solvent of deionized water and organic solvent, and stir thoroughly to form a uniform precursor solution; (2) The precursor liquid described in step (1) is transferred to a closed reactor for uniform precipitation reaction. After the reaction is completed, it is aged to obtain the reaction mixture. (3) The reaction mixture described in step (2) is subjected to solid-liquid separation to obtain nano-oxide precursor and mother liquor respectively; the nano-oxide precursor is washed and the washing liquid is collected, and then the nano-oxide precursor is dried and calcined in sequence to obtain nano-oxide; (4) Add supplementary medium to the mother liquor in step (3) to obtain circulating mother liquor; then repeat steps (2) and (3) as circulating mother liquor for recycling.

4. The method according to claim 3, characterized in that, The soluble rare earth salts mentioned in step (1) include at least one of rare earth nitrate salts, rare earth chloride salts, rare earth sulfate salts, or rare earth acetate salts. And / or, the rare earth element in the soluble rare earth salt of step (1) includes at least one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu; And / or, the rare earth ion concentration in the precursor solution in step (1) is 0.02 mol / L to 0.4 mol / L; And / or, the precipitant in step (1) includes urea; And / or, the structure directing agent in step (1) includes polyvinylpyrrolidone; And / or, the molar ratio of the precipitant to rare earth ions in step (1) is 15:1 to 40:1; And / or, the concentration of the structure-directing agent in the precursor solution in step (1) is 5 g / L to 100 g / L; And / or, the organic solvent in step (1) includes at least one of ethylene glycol, glycerol, methanol or isopropanol; And / or, the organic solvent in step (1) accounts for 5% to 30% of the volume of the precursor solution.

5. The method according to claim 3 or 4, characterized in that, The structure-directing agent in step (1) includes PVP-K90; And / or, the amount of the structure-directing agent added in step (1) is 10 g / L to 50 g / L; And / or, the molar ratio of the precipitant to rare earth ions in step (1) is 18:1 to 25:1; And / or, the organic solvent in step (1) includes at least one of ethylene glycol or methanol; And / or, the organic solvent in step (1) accounts for 10% to 20% of the volume of the mixed solvent.

6. The method according to any one of claims 3 to 5, characterized in that, The gradient heating in the homogeneous precipitation reaction in step (2) includes a first stage of heating, a second stage of heating, and a third stage of heating performed sequentially; The first stage of the gradient heating is heated to 70℃~80℃, and the holding time is 1h~2h. The second stage of the gradient heating process has a heating temperature of 80℃~90℃ and a holding time of 1h~6h. The third stage of the gradient heating process has a heating temperature of 90℃~100℃ and a holding time of 1h~5h. And / or, the heating rate of the gradient heating is 0.5℃ / min to 5℃ / min.

7. The method according to any one of claims 3 to 6, characterized in that, The aging time after the uniform precipitation reaction in step (2) is 12h~24h.

8. The method according to any one of claims 3 to 7, characterized in that, The centrifugation speed for solid-liquid separation in step (3) is above 8000 rpm; And / or, the centrifugation time for solid-liquid separation in step (3) is 10 min to 60 min; And / or, step (3) washing the nano-oxide precursor includes: washing at least three times alternately with deionized water and anhydrous ethanol; And / or, the drying temperature in step (3) is 60℃~80℃, and the time is 8h~15h; And / or, the calcination temperature in step (3) is 300℃~1200℃, and the time is 1h~4h; And / or, the calcined nano-oxides in step (3) include at least one of Y2O3, Yb2O3, CeO2, La2O3, Gd2O3, Tb4O7, Lu2O3, Ni2O3 or Fe2O3.

9. The method according to claim 8, characterized in that, When the nano-oxide in step (3) is Y2O3 or Yb2O3, the calcination temperature is 850℃~950℃; And / or, when the nano-oxide in step (3) is CeO2, the calcination temperature is 750℃~850℃; And / or, when the nano-oxide in step (3) is La2O3, the calcination temperature is 800℃~900℃; And / or, when the nano-oxide in step (3) is Gd2O3 or Tb4O7, the calcination temperature is 650℃~750℃; And / or, when the nano-oxide in step (3) is Lu2O3, the calcination temperature is 650℃~750℃; And / or, when the nano-oxide in step (3) is Ni2O3 or Fe2O3, the calcination temperature is 350℃~450℃.

10. The method according to any one of claims 3 to 9, characterized in that, The mother liquor is recycled and reused 1 to 3 times in step (4).

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